1. Field of the Invention
The present invention relates generally to the fields of immunology, bacteriology and molecular biology. More particularly, the invention relates to methods for screening and obtaining vaccines generated from the administration of expression libraries constructed from a Chlamydia psittaci genome or corresponding homologs from other Chlamydia species. In particular embodiments, it concerns methods and compositions for the vaccination of vertebrate animals against Chlamydia bacterial infections, wherein vaccination of the animal is via a protein or gene derived from part or all of the genes validated as vaccines.
2. Description of Related Art
Intracellular bacteria of the genus Chlamydia are important pathogens in both man and vertebrate animals, causing blindness in man, sexually transmitted disease, and community-acquired pneumonia, and most likely act as co-factors in atherosclerotic plaque formation in human coronary heart disease.
Ubiquitous Chlamydia (C) psittaci infections in cattle cause mastitis, infertility and abortion. A primary economic impact of Chlamydia in dairy cattle is the loss of milk production and quality. Serological evidence for infection with ruminant Chlamydia psittaci is found in virtually all cattle (Kaltenbock et al., 1997). These infections typically do not cause overt signs of disease, but under stress of the host animal may elicit transient inflammation of the mammary gland and uterus. These stress-related herd health problems, while not clinically pronounced, result in major losses for animal agriculture due to reduced output and quality of animal products like milk.
Most existing vaccines for the treatment of bacterial infections are composed of live/attenuated or killed pathogens (Babiuk, 1999). Live/attenuated vaccines present the risk of residual, or reacquisition of, pathogenicity, and are associated with a high cost of production. In addition, efficacious live/attenuated vaccines cannot be developed against many pathogens, or are impractical to produce. Killed pathogens typically have less utility than live/attenuated vaccines, as they are not usually effective in eliciting cellular immune responses. An alternative is subunit vaccines that consist of one or a few proteins of the pathogen (Babiuk, 1999; Ellis, 1999). The proteins being developed for these vaccines are typically based on a dominant immune response in infected hosts, and/or on surmised importance in the disease process. Due to the high genetic complexity of bacteria or protozoa, the empirical approach to identify these proteins often requires extensive research on the pathogen's biology and produces a small, biased set of potential vaccine candidates. However, this is currently the only practical method when proteins are the commodity for testing a vaccine.
The development of genetic (DNA) immunization (Tang et al., 1992) not only offers a new method of vaccine delivery, but also enables a new, unbiased, approach to vaccine discovery. The inventors have proposed that the whole genome of a pathogen could be searched for protein vaccine candidates by directly assessing protection from challenge, termed expression library immunization (ELI) (U.S. Pat. No. 5,703,057, specifically incorporated herein by reference). It involves making an expression library representing the whole genome of the pathogen in a genetic immunization vector. The library is subdivided into smaller groups, and DNA from each library is used to vaccinate animals that are subsequently challenged. The advantage of this approach is that all of the potentially protective genes could be discovered and used in any useful combination to reconstitute a vaccine devoid of non-protective, immunopathological, or immunosuppressive antigens. The potential of ELI was demonstrated in a murine Mycoplasma pulmonis infection, against which random M. pulmonis libraries were protective (Barry et al., 1995). Since then, others have reported on protective libraries (Brayton et al., 1998; Piedrafita et al., 1999), but the reduction of these libraries to individual genes has not been demonstrated.
As described above, the widespread human and animal infections by the genus Chlamydia represents a particular challenge for vaccinology. Chlamydia psittaci infections in cattle cause mastitis, infertility and abortion. A primary economic impact of Chlamydia in dairy cattle is the loss of milk production and quality. Thus, an effective vaccine against Chlamydia bacterial infections in cattle would be of great economic importance. However, there presently have been no effective vaccines developed against any Chlamydia. 